¹H NMR Spectral Simplification with Achiral and Chiral Lanthanide Shift Reagents. IV. Metaxalone, 5-(3,5-Dimethylphenoxymethyl)-2-oxazolidinone; Evidence for Multidentate Chelation

Abstract

The 60 MHz ¹H NMR spectra of racemic metaxalone, 1, have been studied in CDC1₃ solution at 28° with the achiral shift reagent tris(6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedionato)europium(III), 2, and the chiral reagents tris[3-(trifluoromethylhydroxymethylene)-d-cam-phorato]europium(III), 3, and tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium(III), 4. Reagent 3 produced modest observable enantiomeric shift differences, ΔΔδ, for the CH₂0, aryl methyl, aryl H₂,6 and the NH siqnals. Although reaquent 4 produced small or no observable ΔΔδ for the CH₂0, aryl methyls or aryl protons. strikingly qreater valuesof lanthanide induced shift, Δδ, as well as ΔΔδ, were found for the NH signal using 4 relative to 3. Analytical feasibility for direct optical purity determinations of 1 with 0 using this NH siqnal sclould allow detection of 74% of the minor enantiomer or less. Results are discussed ir terms of potential bidentate or tridentate chelation of 3 by 1 makinrl a greater contribution than for 4.